Equalized amplifying tube



May 16, 1933.

E. H. KURTH 1,909,411

EQUALIZED AMPLIFYING TUBE Filed NOV. 13, 1928 OUTPUT In z/eniar Edward2/. Zurzk.

.s'rATEs. PATENT OFFICE cuit, and also, as

Patented May 16, 1933 OF'PASADENA, cAIJIFoRNIA, ASSIGNTOR, ny'nmncr ANDimsnn Ass'IGn ENTs; TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEWXORK',

. Y, 'a'congonn'rronor nnw YORK.

he output-and pu e nt h r y.

unil teral.in. pe t 9 .Aai well k o In the coupling existing between theelements of the neutralized; or in, other words, which is truly Yordinary; tube, and,particularly between the plateand grid, cause theamplifier to be inherently unstableand likely to break lnto undesirable.oscillation, this effect increasingl with the eificiency of theoscillation cir- 4 ,the circuit .is adjusted to higher frequencies. Y 1

"A number- ,01 systems have been devised and practiced to .prevent or.neutralize such oscillations, among the best and most common F of whichmay .be mentioned the system, (exemplifiedin the well known neutrodyeerr-'- cuit) which involves the feedingback of a small quantity ofenergy external of the tube, thisene rgy being suitable in amount andinternal plate to grid feed-back of the three element tube. This energy.is ordinarily conducted between selected points of suitable phaserelationship intheoutput and input circuits through a small. condenser,the capacity of which is adjustable to control the quantity of energypassed. An amplifying system embodying this principle, however, is notequally well neutralized for all frequencies because of an inherent lackof symmetry in the circuit and to the unavoidable presence of inductanceand stray capacity in the feed-back condenser ,connection, which produce"unbala'nfc ed electro-magnetic and electro-static couplingeifects and aconsequent tendency to ward oscillation. In other words, theneutralizing feed-back current does not pass overa circu t electricallyidentical under all conditions with that passing the originalfeedbaclr'current within the tube. These two mem airfrnmyme 'runn inpplication fi le d November-13,1928. am ne-319,151.

relates -to.thermionic.amplifying,tubes,and is particularlyconcerned thecapacitive feed-back paths maypossibly be anade,el ectrically equivalentfor, the amplificatiomof; one frequency, but forv the-amplification offaband of frequencies only. 'a-compromiswmayabe made in this adjustment.It is a well: known fact to t o se familar with the analytical theory.of these circuits, as-it known anyone whoyhas attempted to a'djustathemoperation, that they cannot operate perfeetly over a wide bandoffrequenciessuch, for instance, as is commonly used in broadcast work. HThe primary object ofthe present invention may-now? be stated to be theprovision of an amplifier tube and system which is-inherently equalizedandunilateral for all frequencies and conditions. -j Withthis-preliminary discussion-of the; problem in mind,'I shall'proceed toadetaileddescrlption of my invention, fromwhich its various advantagesand features of improvement will become apparent. For this purpose Irefer to the accompanying drawing, in which:

Fig. 1 is a diagrammatic view showing the elements of the amplifier tubein elevation;

Fig. 2 is a diagrammatic plan view of the elements of the tube; and

Fig. 3 is a suitable electrical amplifier circuit for the tube.

It will be understood that the specific form and arrangement of theelements of the amplifier tube now to be described are but illustrativeof the invention by way of show-- ing one typical means in which it maybe carried out in practice; but that this specificarrangement is notcontrolling on the broad invention, which'may be embodied in anyphysical form or arrangement having the hereinafter specified electricalconstants.

Referring now to the drawing, Figs. land 2 illustrate diagrammaticallythe elements of the amplifier tube, which will be understood to bemounted within a suitable evacuated enclosure, shown at V in Fig. 2.These .ele-

are identical in size and form, and are sym.- metricallylowted Withrespect to the other elements loffthe tube. The two Yinterlocked 15grid's'Gland G2p'r'ovide a common compartment 12 in the center of whichthe filament F is mounted, the filament being. accurately located sothat equal and opposite changes in the potentials of the two' gridsiwillresult."

2 in equal and opposite changes in plate potentials. The two" platesPland P2 are mounted-in the two outer compartments 13' and 145-respectively, in such a manner that thefour plate-to-gridstructurecapacities C1,

255 G2," C3 and C4, indicated in FigiQfare all equal to' one another.-=Each of these several capacities may beconsideredas embracing the totalcapacitive couplingeffect existingbetween a-plate and one of.the gridstructures .01: t-alienas a WllOlG, including not'o'n-ly the adjacent'surface 10-orl 1-1, asthe case may be, but also the end portionsand the remote porti'onon the; opposite'sideof the filament.

Of course, the capacity existing between the plate and the adjacentsurfaces of the grid structure hasafar greater 'effect than does thecapacity existing-between theplate and the remote portions" of the gridstructure, which may be entirelynegligible-for practical purposes.

- ltwvill be noted that theoretically the exact equality of capacitieswill not be achieved by a perfectly 'centrallocation of each plate inits respective compartment, the best position in the arrangementofpFigs. 1 and 2 being found with-each plate a little nearer tothe'inner than to the outer adjacent grid surface. This eccentricity inplate location results from-a slight additional capacity due to thecurved ends 15 of the outer grid surfaces. If, however, the edges-of theplate are not too close to the curved'ends -15 of the grid structure,compared with the space ing of the 1 plate and gri'd'surfacesthemselves,this eccentricity may'be'so small asto be negligible for all practicalpurposes, and the central location 'of-th'e plate maybe used."

It will be apparent that the outer or equalizing portions 11 ofthe-grids need notbe.

pervious. to electrons, and therefore need nothave-thesamecharacteristic grid structure as the plate controlling portions 10;but

may take any form' convenient for manufacture so long as the equalityofcapacitiesis maintained.- And further, the end portions .c,age, infact, is only a suggested form for manufacture, and may. bevaried informand.

arrangement atwill so longasthe specified" electro-static relations aremaintained;

In order to minimize capacitive and" inductive-relations between theleads from the elements of the tube, I prefer to bring leads 20=and21fromhtheiwo. grid structures out of one end of the enclosure, and tobring the plate leads '22 and="23-=and'-the-filamentleads 24a'nd25out ofthe other end.' As-mmatter: of fact, the capacitive relation existingtween-the plateau-dgrid leads" from the' tube when theseleads-arebroughtxout iir relatively close relationmay be utili'zed'fifiavariational physicalembodiment of the invention. In this case-the gridleads-themselves serveas the equalizing grid" portions,- and newbalanced-with respect to the plate I loads as to givethe desiredcapacitive rel'a tions for complete'equalizati'om The actual-design ofthe element'szin an specificcasewill depend upon the, characteristicsdesired in the tubeforits particu lar appl cation, and as theprinciplesforsuch design are wellunderstood inthe art, no descriptionthereof will be herein-1 re= quired- A circuit suitable for theapplicationof this device in-the amplification of radio fre= quencyenergy is shown in Fig; 3; The two grids G1 and G2 are connectedto theoppoa site ends of the input impedance, which may" comprise a continuousinductive winding'30,- no paralleled by a variable tuning condenser*31,.and grounded at its center pointthr'oughia: filament return lead 32having'aresistance 33 and a G-battery supply 34'; The" two'- plates P1and P2. are connected to the opposlte ends of an output Winding 35,grounded at 111966111261 through a filament return lead 36 to the-Bbattery supply. The filamentF" lS grounded through its heating power;source,as will be understood.

The resistance 33,- which may be, say, of a few hundred ohms, isprovided for the purpose of sup'ressing oscillations which maydevelop'in the circuits formed by the halfsections of the inputinductance 30 andsthe 125 shunted grid-to-filament capacities of the,tube. These oscillations are of a frequency independent of the settingof tl1etuning'con-. denser, and do not cause squeals or whistlesr due toheterodyning with the input energy; 136' but are neverthelessobjectionable by reason of loading the tube and decreasing itsefficiency as an amplifier. Inclusion of the resistance 33, however,effectively suppresses these oscillations, while not lessening theefficiency of the circuit for the amplification of energy having afrequency for which the input circuit is tuned. This fact is obviousfrom the consideration that the potential difference developed upon thegrids across the input impedance is independent of the value of thisresistance; and the two components of the current which may be thoughtof as flowing through the resistance are equal and opposite and thuscancel one another.

This circuiting arrangement will be recognized to embody the generalprinciples of the conventional push-pull type of amplifier, the generaloperation of which is understood and will require no detaileddescription here. The novel characteristics of the system will becomeapparent from the following considerations. As in the genuine push-pullcircuit, the two plates, being at the opposite ends of their circuitimpedance, are always 180 out of phase, or in other words the pontentialof one plate reaches its maximum value as the potential of the otherplate reaches its minimum value, and vice versa. It may now be seen thatdue to the peculiar grid structure, by which each grid is provided witha portion adjacent and in equal electrostatic relation to each of theplates, each grid is always under the balanced electrical influence ofthe two equally and oppositely charged plates, and can there forereceive energy from or be affected by neither. The consequence of thisarrangement and its unique advantage is that no 1 current can flow toeither grid as a result of any variation in the potential of the plate,or following a change in the frequency of this variation. Moreover, thearrangement is such that the entire system is perfectly symmetrical, andis therefore truly equalized and unilateral for any possible conditionsthat may be imposed.

It will be understood that the herein detailed embodiment is to beconsidered merely as illustrative of and not restrictive on the broaderclaims appended hereto, for various changes in design and arrangementmay be made without departing from the spirit of the invention or fromthe scope of the said claims.

I claim:

1. A thermionic device comprising, a pair of spaced anode plates, athermionic source located therebetween, a pair of interlocked gridstructures, each surrounding the thermionic source and one of theplates, and the plates to grid capacities all being substantially equalto one another.

2. A thermionic device comprising, a pair of spaced anode plates, athermionic source located therebetween, a pair of'int'e'rlocked eachproviding .a plate-controlling portion adjacent the inner face of theother plate,

and the plate to grid capacity, between each plate and each ofthe gridstructures'asa whole being equal to one, another.

3. A thermionic vaccum tube device comprising, a pair of spaced anodes,a thermionic source located therebetween, and a pair of grid structurescomprising interfitting spirals each surrounding the thermionic sourceand one of the anodes, the anode to grid capacities between the anodesand each of the spiral grid structures being substantially equal to oneanother.

4. A thermionic device comprising an electrode structure including acathode, two anodes, and two grids, said grids having overlappingportions forming a central enclosure surrounding said cathode andportions forming outer enclosures, each outer enclosure surrounding oneof said anodes.

5. A thermionic device comprising an electrode structure including acathode, a pair of spaced anodes, and two grids, each of said gridscomprising one portion having lateral wires extending completely betweensaid cathode and each of said anodes and another portion having lateralwires extending exteriorly of an anode over an area greater than thesurface of the anode.

6. A thermionic device comprising an electrode structure including acathode, a pair of spaced anodes, and a pair of interfitting gridshaving grid laterals forming inner partitions between both of saidanodes and said cathode and having other grid laterals forming outerpartitions beyond the surfaces of said anode.

7. A thermionic device comprising an electrode structure including acathode, a pair of spaced anodes, and a pair of interfitting gridshaving grid laterals formin inner partitions between both of said ano esand said cathode and having other grid laterals forming outer partitionsbeyond the surfaces of said anodes, said outer partitions, anodes andinner partitions being in equal electrostatic relation whereby each gridis under the balanced influence of said anodes.

8. A thermionic device comprising an electrode structure including acathode, two anodes, and a pair of oval-shaped wire grids arranged toform two outer enclosures of equal area and a common central enclosureof lesser area, said cathode being located in said central enclosure,each of said outer enclosures containing one of said anodes.

9. A thermionic device comprising an electrode structure including acathode, a pair of spaced anodes, and a pair of oval-shaped Iwiresgrids: arranged to form two outer-"encl'osuresandas commoncentralenclosure said cathodebeing-:bcatedin said centralenclorsuregzfleach outer enclosure?containingione of saidzanodegfliagridlaterals of said central 7 enelbsure'bei'ng a multiple of the grid lat---er;als=.of':said: outer: enclosures; 1

1 1m Witness that I claim the-foregoing I havet hereunfioisubscribed myname this 29th 10 day ofAugust,1928. 5 g Y Y Y ED WARD-HKURTH==

